1. Field of the Invention
The present invention relates generally to devices for ventilating buildings, and in particular to such devices used to ventilate agricultural buildings used for the housing of livestock.
2. Background
Agricultural buildings used for the housing and raising of livestock, and in particular poultry, generally require ventilation to control, among other factors, temperature, humidity and air quality. Most ventilation systems are active, that is, they use a motorized mechanism, such as a fan or fans to exhaust the "old air" and replace it with fresh outside air. Passive systems are also used and have the advantage, as compared to active systems, of not requiring the expenditure of additional energy to accomplish the needed air exchange.
Passive systems rely upon the natural convective flow of air that results from the temperature differential that exists between the warm interior building air and the cooler air outside of the building. Passive systems generally include exhaust vents, typically located on the roof of the structure, to exhaust the warm interior air as it rises, and intake vents, generally located on the exterior walls of the building, that permit the replacement of the warm interior air by the cooler outside air.
In northern climates, due to their location on the roof, exhaust vents can become blocked or frozen shut with snow or ice, which blockage thus, prevents air exchange. In addition, as passive systems are essentially dependent upon natural conditions to provide for air flow and exchange, and as such air flow can be greater than, or less than the optimum flow rate that may be desired at a particular point in time, it is important that a passive system include means for regulating the rate of air flow to the extent permitted by the natural conditions.
Accordingly, it would be desirable to have a passive ventilation system the effectiveness of which is not easily compromised by the effects of snow and ice. It would also be desirable to have such a passive ventilating system that provides for the regulation of air exchange.